Patients with chronic obstructive lung disease have a high incidence and wide variety of cardiac arrhythmias. These arrhythmias are often clinically significant and may be life threatening. Although they occur particularly in the context of acute respiratory failure, arrhythmias are not infrequent in clinically stable patients. The relatively high incidence of sudden arrhythmias seen in acute respiratory failure are associated with a very poor prognosis, in particular, ventricular premature beats and multifocal atrial tachycardia. Long-term electrocardiographic monitoring is valuable in increasing the detection of these arrhythmias and in assessing their clinical significance and response to therapy. The mechanisms producing these arrhythmias are poorly understood and probably multiple. However, disturbances of blood gases, blood pH, and electrolytes or the presence of cor pulmonale or associated coronary artery disease is probably important. The therapy of these arrhythmias must include efforts to improve the patient's ventilatory status as well as careful use of standard antiarrhythmic drugs. Further investigation is needed to define the mechanisms, determine the prognosis, and improve the therapy of the arrhythmias found in chronic obstructive lung disease.